This invention generally pertains to a method and a device for measuring portal blood pressure, and more particularly pertains to a method and a device that use an inflatable balloon inserted into the esophagus.
A high pressure gradient typically exists across a diseased or damaged liver, between the portal and hepatic veins. The development of this restriction through the liver causes blood to bypass the liver and forces blood into collateral blood vessels within and around the upper stomach and lower esophagus. As a result, esophageal and gastric veins bulge inside the gastrointestinal lumen and are visible as gastrointestinal varices under upper gastrointestinal endoscopy. If the portal blood pressure exceeds 21 mmHg, the varices often rupture and produce a life threatening hemorrhage. However, this often fatal and always serious bleeding can be prevented by prophylactic drug therapy.
Accordingly, patients with liver disease are placed under surveillance and watched for portal hypertension and risk of gastrointestinal bleeding. If their portal pressure is greater than 22 mmHg or their portal-hepatic pressure gradient is greater than 12 mmHg, the patients are treated with beta blockade. During this drug treatment, the portal blood pressure of a patient remains under watch. Further surveillance determines if they are properly responding to beta blockade, determines if there is a need for other drugs to reduce portal blood pressure, and generally monitors the effect of therapy on the patient. The more acute and severe the patient's liver disease, particularly if the patient is suffering from upper gastrointestinal bleeding, the more important is the measurement of portal pressure and the patient's response to therapy.
The traditional methods of measuring portal pressure require entry into an hepatic or portal vein. The percutaneous method can be applied on ambulatory or hospitalized patients who do not have a bleeding diathesis or advanced cirrhosis with portal hypertension. In this technique, under local anesthesia, a fine gauge needle is inserted into the veins under fluoroscopic control. In a fashion similar to that for performing percutaneous cholangiography, the needle is manipulated into a portal vein and its position confirmed by injecting a small amount of contrast. The portal pressure is then measured. The needle is then manipulated into a hepatic vein, also confirmed by injection of a small amount of contrast, and the hepatic venous pressure is measured. The difference between the portal and hepatic pressure is calculated as the portal-hepatic pressure gradient. Gradients greater than 12 mmHg indicate a risk of variceal hemorrhage.
Measurement of portal pressure by transvenous catheterization is done in a similar fashion. The hepatic vein is entered with a standard cardiovascular catheter through either a femoral, internal jugular, or medial antecubital approach under local anesthesia. The catheter is advanced under fluoroscopy into a hepatic vein and wedged closed, typically with a balloon catheter. With the vein blocked, there is a stasis column of blood extending from the hepatic vein to the portal vein in patients with cirrhosis, and portal pressure is similar or identical to the occluded or wedged hepatic venous pressure. The non-wedged hepatic venous pressure or inferior vena caval pressure is then measured and the difference is calculated as the portal-hepatic pressure gradient.
Both of these preceding methods are expensive procedures using complex methods and specialized techniques. They are rarely used by gastrointestinal endoscopists. It would be of great value if portal pressure could be more easily measured during gastrointestinal endoscopy, perhaps in a more simple and less obtrusive fashion.
Measurement of portal pressure should be differentiated from pressure within esophageal varices and the measurement thereof. Pressure in portal-systemic collateral vessels (esophagogastric varices) is related to but not identical to portal pressure because the collateral vessels are part of a resistance loop between pressure in the portal vein and the systemic exit point of the collateral vein. Furthermore in the clinical situation where physiologic variables (changes in blood volume) or drug therapy (beta blockade) directed at changing (reducing) portal pressure and splanchnic blood inflow are operating the relationship between portal pressure and variceal pressure would be variable. Consequently in any individual situation the relationship between variceal pressure and portal pressure cannot be known without a comparative measurement. Therefore direct measurement of portal pressure is essential.